An optical isolator (sometimes referred to as an optocoupler) provides isolation between a digital input circuit and a digital output circuit. A typical optical isolator has a light-emitting diode (LED) electronically coupled to the input circuit. The LED is optically coupled across an electronically isolating gap to a photodetector device, such as a photodiode. The photodiode receives an optical signal from the LED and converts the signal to an electric current pulse. Typically, this current pulse is amplified in a switching circuit coupled to the photodiode and delivered as a digital output signal to the output circuit.
It has been observed in systems with optocouplers that there are times when apparently random signal errors arise. Such "glitches" are not found in all systems, nor do they occur with sufficient regularity that their source can be readily identified. In fact, workers have for many years sought to improve the reliability of digital data and eliminate such random errors.
It is, therefore, desirable to provide an integrated photodetector for an optical isolator having improved reliability at high speeds over a broad range of LED speeds and despite power supply noise.